ISOCAM Interactive Analysis User's Manual Version 5.0 - ISO - ESA

20.15. ADVANCED PROJECTION 259
• corr dark will ignore column 24 if /dead col is set, otherwise it will call corr col24 to
fill it after performing dark correction on .CUBE.
• corr flat will ignore column 24 if /dead col is set, otherwise it will call corr col24 to fill
it after performing flat correction on .IMAGE (or .CUBE if the keyword /cube is set).
Of course, at any stage in CIA processing you can fill column 24 yourself with corr col24.
Forexampletofillcolumn24in.CUBEand.IMAGE
corr_col24, pds
To fill only .CUBE or only .IMAGE then set the keyword /cube or /image respectively.
20.15 Advanced projection
The projection is method is probably the best choice for creation of the raster MOSAIC (see
Section 20.4 for other methods). There are a number of useful options available for projection
and indeed the CIA projection routines have other purposes aside from the create of raster
MOSAICs.
20.15.1 Distortion correction
There are a couple of options when it comes to projection and distortion correction. These can
be specified as raster scan keywords. Note that projection is actually performed by the lowerlevel
routine projette and the C++ executable projection. Keywords given to raster scan are
passed to projette, so it may be a good idea to take a look at the online help for both these
routines.
• Perform the projection but create the raster MOSAIC without distortion correction:
CIA> raster_scan, raster_pds, /nodisto
• Perform the projection using drizzling:
CIA> raster_scan, raster_pds, shrink=0.7
• Perform distortion correction, but give an alternative distortion file:
CIA> raster_scan, raster_pds, dist_file=’lw3asr10.dis’
20.15.2 Weighted mean option
Normally, the weighting factor per EXPOSURE pixel is computed as a function of the good
number of readouts stored in .CCIM.NPIX (see Section 15.5.8). However, in case of systematic
errors (e.g. due to the flat-field uncertainty at the edge of the detector or unstabilized pixels)
better results might be achieved by using the standard error instead. This error is computed as
standard error =
σ √ n
=
.CCIM.RMS
√
.CCIM.NPIX
(20.1)
The following script gives some examples how to use the different methods; raster pds, a
short 2 × 2 raster, has been dark-corrected, deglitched, transient corrected and flat-fielded with
the library flat-field for all but the last example, which was flat-fielded with a sky flat-field.